Potassium hydrogenacetylenedicarboxylate
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Preferred IUPAC name
But-2-ynedioic acid
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| Other names
2-Butynedioic acid
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3D model (JSmol)
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| ChEBI | |
| ChemSpider | |
| ECHA InfoCard | 100.005.033 |
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PubChem CID
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| Properties | |
| C4H2O4 | |
| Molar mass | 114.06 g·mol−1 |
| Appearance | Crystalline solid |
| Melting point | 175 to 176 °C (347 to 349 °F; 448 to 449 K) (decomposes) 180–187 °C (decomposes) |
| Hazards | |
| R-phrases (outdated) | R25 R36/37/38 |
| S-phrases (outdated) | S26 S45 |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| Infobox references | |
Acetylenedicarboxylic acid or butynedioic acid is an organic compound (a dicarboxylic acid) with the formula C4H2O4 or HO2C-C≡C-CO2H. It is a crystalline solid that is soluble in diethyl ether.
The removal of two protons yields the acetylenedicarboxylate dianion C4O42−, which consists only of carbon and oxygen, making it an oxocarbon anion. Partial ionization yields the monovalent hydrogenacetylenedicarboxylate anion HC4O4−.
The acid was first described in 1877 by Polish chemist Ernest Bandrowski. It can be obtained by treating α,β-dibromosuccinic acid with potassium hydroxide KOH in methanol or ethanol. The reaction yields potassium bromide and potassium acetylenedicarboxylate. The salts are separated and the latter is treated with sulfuric acid.
Acetylenedicarboxylic acid is used in the synthesis of dimethyl acetylenedicarboxylate, an important laboratory reagent. The acid is commonly traded as a laboratory chemical. It can also be reacted with sulfur tetrafluoride to produce hexafluoro-2-butyne, a powerful dienophile for use in Diels-Alder reactions.
Hydrogenacetylenedicarboxylate (often abbreviated as Hadc or HADC) is a monovalent anion of acetylenedicarboxylic acid with the formula C4HO4− or HO2C-C≡C-CO2−. The anion can be derived from acetylenedicarboxylic acid by removal of a single proton or from the acetylenedicarboxylate dianion by addition of a proton. The name is also used for any salt of this anion. Salts of this anion are of interest in crystallography because they contain unusually short and strong hydrogen bonds. In many crystalline salts (with the exception of the lithium one), the HADC units form linear chains connected by strong hydrogen bonds. Each carboxylate group is usually planar; but the two groups may lie in different planes due to rotation about the C-C bonds. They are coplanar in the hydrated salts NaHC4O4·2H20 and CsHC4O4·2H20, nearly coplanar in the guanidinium salt [C(NH2)3]+ · C4HO4−, but off by 60 degrees or more in other salts such as anhydrous potassium hydrogenacetylenedicarboxylate.
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